1. FIELD OF THE INVENTION
The present invention relates to a process for producing an acicular goethite having fine particle size which can be used to produce magnetic particles having high coercive force.
2. DESCRIPTION OF THE PRIOR ARTS
Heretofore, it has been known to produce the acicular goethite by adding an alkali ion to an aqueous solution of ferrous salt such as ferrous sulfate to give pH of higher than 11, and oxidizing it with air.
Thus, the conventional process has the disadvantages that it takes a long time for the production and the resulting acicular goethite has large particle size.
Recently, in the magnetic recording medium industry, it has been required to obtain a magnetic powder having high characteristics which can be used in high density. In order to satisfy such requirements, a magnetic powder having smaller particle size and higher coercive force has been required. However, it has been difficult to obtain such magnetic powder having small particle size and high coercive force by the conventional process.
The inventors have studied to overcome the problem and have found that the reaction time can be remarkably shortened by oxidizing a ferrous component with air etc. at a ratio of an anion such as sulfuric ion to ferrous ion such as ferrous sulfate of less than 1 to obtain an acicular goethite having fine particle size and the resultant .gamma.-Fe.sub.2 O.sub.3 has high coercive force.